/Engine/Source/Runtime/Engine/Public/MaterialShared.h
[FGuid](API\Runtime\Core\Misc\FGuid) GetExternalTextureGuid ( const [FGuid](API\Runtime\Core\Misc\FGuid) & ExternalTextureGuid, const [FName](API\Runtime\Core\UObject\FName) & ParameterName, int32 SourceTextureIndex ) const